NIR broadband emitting phosphors for infrared spectroscopy

ABSTRACT

A luminescent material is disclosed with emission in the near infrared wavelength range, the luminescent material including Sc1-x-yAyRE:Crx, wherein MO=P3O9, BP3O12, SiP3O12; A=Lu, In, Yb, Tm, Y, Ga, Al, where 0≤x≤0.75, 0≤y≤0.9. A wavelength converting structure including the luminescent phosphor is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to European PatentApplication 19168890.2 filed Apr. 12, 2019, which is incorporated hereinby reference in its entirety.

FIELD OF THE INVENTION

The invention relates to a luminescent material and to a wavelengthconverting structure.

BACKGROUND

Oomen et al. (J. Solid State Chemistry, vo. 75 no 1 (1988), 201-204),describe the luminescence of the Bi³⁺ ion (6s²) in the metaphosphatesLnP₃O₉ (Ln=Sc, Lu, Y, Gd, La). For Ln=Sc, Lu, Y, Gd the metaphosphateshave a monoclinic structure with four slightly different sites for thetrivalent cations. For Ln=Sc, Lu, Y the Stokes shift of the Bi³⁺luminescence increased with increasing radius of the host latticecation. Concentration quenching of the Bi³⁺ luminescence is observed. Inthe case of GdP₃O₉—Bi³⁺ the excitation energy is transferred to the Gd³⁺ions. LaP₃O₉ adopts an orthorhombic structure with only one siteavailable for the trivalent cations. The different coordination of theBi³⁺ ion leads to a large increase of the Stokes shift of theluminescence. Oomen et al. also reported on the luminescence of the 5s²ion Sb³⁺ in LnP₃O₉ (Ln=Sc, Lu, Y, Gd, La).

Qiyue Shao et al., RSC. Adv., 8 (2018), 12035-12042, indicate that rapidextension of solid state lighting technologies offers the possibility todevelop broadband near-infrared (NIR) phosphor-converted LEDs (pc-LEDs)as novel NIR light sources. In this paper, it is indicated that aNIR-emitting phosphor ScBO₃:Cr³⁺ was synthesized by a high temperaturesolid state reaction method. Phase structure, spectroscopic properties,luminescent lifetime, quantum yield, emitter concentration influencesand thermal quenching behavior of ScBO₃:Cr³⁺, as well as itsapplications for NIR pc-LEDs, were investigated. ScBO₃:Cr³⁺ phosphorsexhibit a broad absorption band ranging from 400 to 530 nm, whichmatches well with the characteristic emission of the blue LED chip.Moreover, Cr³⁺ ions occupy the Sc³⁺ sites with relatively low crystalfield strength in the ScBO₃ host, and therefore ScBO₃:Cr³⁺ phosphorsshow intense broadband emission peaking at ˜800 nm upon excitation at460 nm, originating from spin-allowed ⁴T₂→⁴A₂ transition of Cr³⁺ ions.The optimum Cr³⁺ concentration was determined to be 2 mol % with aquantum yield of 65%. A broadband NIR pc-LED prototype device wasfabricated by the combination of ScBO₃:Cr³⁺ phosphors and a blue LEDchip, which showed a maximum NIR light output power of 26 mW and acorresponding energy conversion efficiency of 7%.

Veeramani Rajendran et al., Optical Materials X, 1 (2019), 100011,indicate that the development of phosphor-converted technology-basedbroadband near-infrared light source for miniature spectrometers toperform spectroscopy applications has recently attracted remarkableattention among researchers in the academe and industry. The transitionmetal element Cr³⁺-activated luminescent materials act as the potentialcandidates to meet the demands for increased near-infrared lightspectral distribution. In this document, the most recently developedbroadband near-infrared phosphors activated by Cr³⁺ are listed andclassified according to their major chemical element constituents. Inaddition to the luminescence mechanism of Cr³⁺, the association betweenthe number of crystallographic sites and spectral distribution ofnear-infrared light is mainly reviewed with the example of knownnear-infrared phosphors, which may be helpful in exploring futurebroadband near-infrared phosphors. The performance-evaluating parametersof phosphor-converted near-infrared light-emitting diode are discussedand compared with those of known broadband near-infrared phosphors forspectroscopy applications.

SUMMARY OF THE INVENTION

Semiconductor light emitting diodes and laser diodes (collectivelyreferred to herein as “LEDs”) are among the most efficient light sourcescurrently available. The emission spectrum of an LED typically exhibitsa single narrow peak at a wavelength determined by the structure of thedevice and by the composition of the semiconductor materials from whichit is constructed. By suitable choice of device structure and materialsystem, LEDs may be designed to operate at ultraviolet, visible, orinfrared wavelengths.

LEDs may be combined with one or more wavelength converting materials(generally referred to herein as “phosphors”) that absorb light emittedby the LED and in response emit light of a longer wavelength. For suchphosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted bythe LED that is absorbed by the phosphors depends on the amount ofphosphor material in the optical path of the light emitted by the LED,for example on the concentration of phosphor material in a phosphorlayer disposed on or around the LED and the thickness of the layer.

Phosphor-converted LEDs may be designed so that all of the light emittedby the LED is absorbed by one or more phosphors, in which case theemission from the pcLED is entirely from the phosphors. In such casesthe phosphor may be selected, for example, to emit light in a narrowspectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of thelight emitted by the LED is absorbed by the phosphors, in which case theemission from the pcLED is a mixture of light emitted by the LED andlight emitted by the phosphors. By suitable choice of LED, phosphors,and phosphor composition, such a pcLED may be designed to emit, forexample, white light having a desired color temperature and desiredcolor-rendering properties.

In an aspect, the invention provides a luminescent material comprisingSc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=P₃O₉, (BP₃O₁₂)_(0.5),(SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al, where 0≤x≤0.75, 0≤y≤2.

In embodiments, MO is P₃O₉ and 0≤x≤0.5, 0≤y≤0.9. Especially, x is largerthan 0. Hence, especially 0<x. Further, in embodiments 0≤y≤1. Inspecific embodiments, 0<x+y≤1. Especially, x>0 (in view of theavailability of Cr³⁺). Especially, in embodiments 0≤y≤1. As x isespecially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, in embodiments 0<x≤0.75, and 0≤y≤0.9. In specificembodiments, 0<x≤0.5, and 0≤y≤0.9.

In embodiments, MO is (BP₃O₁₂)_(0.5) and 0≤x≤0.75, 0≤y≤1.8. Especially,x is larger than 0. Hence, especially 0<x. Further, in embodiments0≤y≤1. In specific embodiments, 0<x+y≤1. Especially, x>0 (in view of theavailability of Cr³). Especially, in embodiments 0≤y≤1. As x isespecially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, in embodiments 0<x≤0.75, and 0≤y≤0.9. In specificembodiments, 0<x≤0.5, and 0≤y≤0.9.

In embodiments, MO is (SiP₅O₁₉)_(0.34) and 0≤x≤0.2, 0≤y≤2. Especially, xis larger than 0. Hence, especially 0<x. Further, in embodiments 0≤y≤1.In specific embodiments, 0<x+y≤1. Especially, x>0 (in view of theavailability of Cr³⁺). Especially, in embodiments 0≤y≤1. As x isespecially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, in embodiments 0<x≤0.2, and 0≤y≤0.9. In specific embodiments,0<x≤0.2, and 0≤y≤0.9.

In embodiments, y=0. Especially, in alternative embodiments y is largerthan 0, like at least 0.01, such as at least 0.02, like at least 0.05,such as at least 0.1.

Further, in specific embodiments A comprises one or more of In, Ga, andAl, such as one or more of In and Ga, like at least In. In alternativeembodiments, A comprises at least Lu.

In embodiments, the luminescent material emits light having a peakwavelength in a range of 700 nm to 1100 nm.

In an aspect, the invention provides a phosphor material including atleast one of Sc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=BO₃, P₃O₉,(BP₃O₁₂)_(0.5), (SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al, where0<x≤0.75, 0≤y≤2 (especially 0≤y≤1), and wherein when MO=BO₃, 0<y (i.e.y>0). In embodiments, the invention provides a phosphor materialincluding at least one of Sc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=P₃O₉,(BP₃O₁₂)_(0.5), (SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al, where0<x≤0.75, 0≤y≤2 (especially 0≤y≤1). As indicated above, especially x islarger than 0. Hence, especially 0<x. Further, as indicated above inembodiments 0≤y≤1. In specific embodiments, 0<x+y≤1. Especially, x>0 (inview of the availability of Cr³⁺). Especially, in embodiments 0≤y≤1. Asx is especially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, as indicated above, in embodiments 0<x≤0.75, and 0≤y≤0.9. Inspecific embodiments, 0<x≤0.5, and 0≤y≤0.9. In embodiments wherein MO is(SiP₅O₁₉)_(0.34), especially 0≤x≤0.2, 0≤y≤1 applies.

In yet a further aspect, the invention provides a wavelength convertingstructure comprising an NIR phosphor material, the NIR phosphor materialincluding at least one of Sc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=BO₃,P₃O₉, (BP₃O₁₂)_(0.5), (SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al,where 0≤x≤0.75, 0≤y≤2. As indicated above, especially x is larger than0. Hence, especially 0<x. Further, as indicated above in embodiments0≤y≤1. In specific embodiments, 0<x+y≤1. Especially, x>0 (in view of theavailability of Cr³⁺). Especially, in embodiments 0≤y≤1. As x isespecially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y≤1. Especially, in further embodiments 0≤y≤0.9.Therefore, as indicated above, in embodiments 0<x≤0.75, and 0≤y≤0.9. Inspecific embodiments, 0<x≤0.5, and 0≤y≤0.9. In embodiments wherein MO is(SiP₅O₁₉)_(0.34), especially 0≤x≤0.2, 0≤y≤1 applies.

In embodiments, when MO=BO₃, 0<y.

As indicated above, especially, x is larger than 0. Hence, especially0<x. Therefore, in embodiment 0<x≤0.75, and 0≤y<1, such as 0≤y≤0.9.

In embodiments, the wavelength converting structure further comprising alight source emitting a first light, the wavelength converting structuredisposed in a path of the first light, wherein the NIR phosphor absorbsthe first light and emits a second light, the second light having awavelength range of 700 nm to 1100 nm.

In embodiments, the wavelength converting structure further comprising asecond phosphor material, wherein the second phosphor material includesat least one of a green phosphor, a red phosphor, and an IR phosphor.

In embodiments, the wavelength converting structure wherein MO is P₃O₉and 0<x≤0.5, 0≤y≤0.9.

In embodiments, the wavelength converting structure wherein MO is(BP₃O₁₂)_(0.5) and 0<x≤0.75, 0≤y≤1.8. Hence, especially x is larger than0. Hence, especially 0<x. Further, as indicated above in embodiments0≤y≤1. In specific embodiments, 0<x+y≤1. Especially, x>0 (in view of theavailability of Cr³⁺). Especially, in embodiments 0≤y≤1. As x isespecially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, as indicated above, in embodiments 0<x≤0.75, and 0≤y≤0.9. Inspecific embodiments, 0<x≤0.5, and 0≤y≤0.9.

In embodiments, the wavelength converting structure wherein MO is(SiP₅O₁₉)_(0.34) and 0<x≤0.2, 0≤y≤2. As indicated above, especially x islarger than 0. Hence, especially 0<x. Further, as indicated above inembodiments 0≤y≤1. In specific embodiments, 0<x+y≤1. Especially, x>0 (inview of the availability of Cr³⁺). Especially, in embodiments 0≤y≤1. Asx is especially larger than 0, y is especially smaller than 1. Hence, inembodiments 0≤y<1. Especially, in further embodiments 0≤y≤0.9.Therefore, as indicated above, in embodiments 0<x≤0.75, and 0≤y≤0.9. Inspecific embodiments, 0<x≤0.5, and 0≤y≤0.9.

In embodiments, the wavelength converting structure wherein MO is BO₃,0<x≤0.5, y>0 and y≤0.9. In embodiments, the wavelength convertingstructure wherein the MO is BO₃, A is Lu and 0.05≤y≤0.25 and0.01≤x≤0.06.

In embodiments, a wavelength converting structure is provided whereinthe NIR phosphor includes at least one of Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02)(x=0, 0.2, 0.3), Sc_(1-x)P₃O₉:Cr_(x) (x=0.02, 0.04, 0.08),Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) (x=0.04, y=0.0; x=0.08, y=0.0; x=0.8,y=0.96), and Sc_(2.88)SiP₅O₁₉:Cr_(0.12). In embodiments, of thewavelength converting structure the NIR phosphor includes 5 wt %Sc_(0.98)BO₃:Cr_(0.02) and 95 wt % Sc_(1.92)BP₃O₁₂:Cr_(0.08).

In specific embodiments, the phosphor material comprisesSc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=BO₃, wherein 0<x≤0.75, 0<y≤1 (thusespecially in fact 0<y<1). Hence, the compound comprises at least one ofLu, In, Yb, Tm, Y, Ga, Al. In further specific embodiments, A at leastcomprises In. Yet further, in specific embodiments, the phosphormaterial comprises Sc_(1-x-y-z)A_(y)MA′_(z)MO:Cr_(x), wherein MO=BO₃,wherein 0<x≤0.75; 0<y<1; 0≤z≤1; 0<y+z<1; wherein A=In, and whereinA′=Lu, Yb, Tm, Y, Ga, Al. Especially, in embodiments z=0. In otherembodiments, z>0.

Instead of the term “luminescent material” also the term “phosphormaterial” may be applied.

The phosphor may comprise a combination of two or more of the hereindescribed phosphors. Two phosphors having the same general formula, buthaving a different composition for A may be different phosphors. Forinstance, Sc_(1-x-y)Lu_(y) BO₃:Cr_(x) may differ from Sc_(1-x-y)In_(y)BO₃:Cr_(x) especially in terms of spectral characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a wavelength converting structure aspart of an illumination device.

FIG. 2 illustrates another embodiment of a wavelength convertingstructure as part of an illumination device.

FIG. 3 is a cross sectional view of an LED.

FIG. 4 is a cross sectional view of a device with a wavelengthconverting structure in direct contact with an LED.

FIG. 5 is a cross sectional view of a device with a wavelengthconverting structure in close proximity to an LED.

FIG. 6 is a cross sectional view of a device with a wavelengthconverting structure spaced apart from an LED.

FIG. 7 shows the emission spectra of each of theSc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (x=0, 0.2, 0.3) phosphors underexcitation of blue light (443 nm).

FIG. 8 shows the powder x-ray diffraction (XRD) pattern of theSc_(0.96)P₃O₉:Cr_(0.04) phosphor.

FIG. 9 shows the emission spectra of each of the Sc_(1-x)P₃O₉:Cr_(0.04)(x=0.02, 0.04, 0.08) phosphors under excitation of blue light (443 nm).

FIG. 10 shows the X-ray powder diffraction patterns of theSc_(1.96)BP₃O₁₂:Cr_(0.04) phosphor.

FIG. 11 shows the diffuse reflectance of Sc_(1.92)BP₃O₁₂:Cr_(0.08)phosphor powder.

FIG. 12 shows the emission spectra of Sc_(1.92)BP₃O₁₂:Cr_(0.08) underexcitation at 443 nm.

FIG. 13 shows the X-ray powder diffraction pattern of theSc_(2.88)SiP₅O₁₉:Cr_(0.12) phosphor.

FIG. 14 shows the emission spectrum of Sc_(2.88)SiP₅O₁₉:Cr_(0.12) underexcitation at 443 nm.

FIG. 15 shows the EL spectrum of a pcLED having a wavelength convertingstructure containing a disclosed NIR phosphor.

Schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION

This specification discloses luminescent materials that are phosphorsthat can emit near-infrared (NIR) radiation, and devices that include awavelength converting structure formed from the luminescent materialsthat are phosphors that can emit NIR radiation. The luminescentmaterials that are phosphors that can emit NIR radiation may be referredto herein as “NIR phosphors,” “NIR phosphor materials,” and/or “NIRphosphor compositions.” For economy of language, infrared rations may bereferred to herein as “light.”

NIR Phosphor Compositions

The luminescent materials are NIR emitting broadband phosphors that canenable pc LED light sources that have improved spectral shapes and lightoutput levels. Higher light output levels are advantageous for manyapplications, including e.g., spectroscopy applications because theyprovide an improved signal-to-noise ratio resulting in more accurate andfaster analysis.

In general, Cr(III) doped phosphors are suitable down-conversionmaterials for pcLEDs that emit in the NIR region (“pc-NIR LEDs”) becauseof the relatively intense absorption bands in the blue to red spectralrange and the large Stokes shift that leads to broad band emission inthe NIR spectral range. While Cr(III) is often incorporated onoctahedral Ga(III) sites in the host lattices, for example galliumgarnet phosphors like Gd₃Ga₅O₁₂:Cr or in La₃(Ga,Al)₅(Ge,Si)O₁₄:Cr typephosphors, incorporation on larger octahedral Sc(III) can further shiftthe broadband Cr(III) emission towards longer wavelengths.

This specification discloses new NIR phosphor compositions from theclass of Cr(III) doped scandium phosphates, borates, borophosphates, andborosilicates that are characterized by acidic oxygen ligandssurrounding the dopant. While not wanting to be bound by any particulartheory, it is believed by the inventor that the acidity is caused by thestrong bonding towards the small and highly charged P⁵⁺, Si⁴⁺ and B³⁺ions. As a consequence the antibonding character towards the higherenergy Cr(III) d states is being reduced, and results in smaller Stokesshifts and higher thermal stability of the emission compared tobroadband NIR gallate, germanate or aluminate phosphors.

In particular, borates of composition REBO₃, phosphates of compositionREP₃O₉, borophosphates of composition (RE)₂BP₃O₁₂, and silicophosphatesof the composition (RE)₃SiP₅O₁₉ are disclosed. Specifically RE may be atrivalent cation that occupies an octrahedrally coordinated latticesite. RE may be chosen from the group of Sc and Cr.

To adjust the absorption and emission properties of the Cr(III) dopedscandium phosphates, borates, borophosphates, and borosilicates, aportion of the Sc can either be replaced by larger sized trivalent Lu,In, Yb, Tm or Y to obtain a spectroscopic shift towards longerwavelength, or by smaller sized trivalent Ga or Al to induce aspectroscopic shift towards shorter wavelength. In this way, a broadcoverage of the NIR emission wavelength range from 700-1200 nm can beobtained by combining the NIR phosphor materials with III-V type primaryLEDs that show emission in the blue, cyan, green or red spectral range.

Sc_(1-x-y)A_(y)BO₃:Cr_(x)

Sc_(1-x-y)A_(y)BO₃:Cr_(x) (A=Lu, In, Yb, Tm, Y, Ga, Al; 0<x≤0.5,0<y≤0.9) shows emission in the 800-890 nm centroid wavelength range if,e.g., excited by blue light. ScBO₃:Cr (y=0) is a phosphor materialdescribed by Blasse and Dirksen (Blasse, G. and G. J. Dirksen (1988).“Scandium borate (ScBO₃) as a host lattice for luminescent lanthanideand transition metal ions.” Inorganica Chimica Acta 145(2): 303-308,incorporated herein by reference in its entirety). In ScBO₃, whichcrystallizes in the calcite crystal structure type, Cr(III) experiencesa weak crystal field and shows emission of the broad-band ⁴T₂→⁴A₂ type.Although LuBO₃ crystallizes in the vaterite structure type, the inventorfound that part of Sc can be replaced by Lu while the calcite structuretype is maintained and the emission band is further shifted to longerwavelengths. This leads to compositions according toSc_(1-x-y)Lu_(y)BO₃:Cr_(x). Preferably, 0.05≤y≤0.25 and 0.01≤x≤0.06.

Because, for some applications, broad emission bands may be preferredfor phosphors applied in pc NIR LED light sources, additional dopingwith the smaller sized Ga(III) can be carried out. This leads tocompositions according to Sc_(1-x-y-z)Lu_(y)Ga_(z)BO₃:Cr_(x).Preferably, 0.02≤y≤0.4, 0.02≤z≤0.6 and 0.01≤x≤0.06. In this case Cr(III)occupies multiple lattice sites with slightly differing sizes,eventually leading to a broadened, composed emission band.

Sc_(1-x-y)A_(y)P₃O₉:Cr_(x)

Emission in the 880-940 nm centroid wavelength range is observed fornovel Sc_(1-x-y)A_(y)P₃O₉:Cr_(x) (A=Lu, In, Yb, Tm, Y, Ga, Al; 0<x≤0.5,0≤y≤0.9) if, e.g., excited by blue light. These polyphosphate phosphorscrystallize in the monoclinic C-type or RhP₃O₉ polyphosphate structure(Hoppe, H. A. (2009). “The phase transition of the incommensurate phasesβ-Ln(PO₃)₃ (Ln=Y, Tb . . . Yb), crystal structures of α-Ln(PO₃)₃ (Ln=Y,Tb . . . Yb) and Sc(PO₃)₃.” Journal of Solid State Chemistry 182(7):1786-1791, incorporated herein by reference in its entirety) or in thecubic AlP₃O₉ or A₄(P₃O₉)₄ structure type where the latter is stabilizedby higher firing temperatures and smaller sizes of A atoms.

Table 1 shows a comparison of the structure types of ScP₃O₉ with lowtemperature (“LT”) vs high temperature (“HT”) firing:

TABLE 1 Comparison of ScP₃O₉ structure types: modification LT-ScP₃O₉HT-ScP₃O₉ structure type RhP₃O₉ AlP₃O₉ Space group C 1 c 1 (No 9) I-4 3d (No 220) No of Sc sites 3 2 Sc1—O 2.068-2.102 2.082 (Angstr.) Sc2—O2.072-2.097 2.071 (Angstr.) Sc3—O 2.037-2.108 (Angstr.)

The low temperature modification shows three crystallographicallyindependent Sc sites that can be populated with Cr while the hightemperature modification shows two crystallographically independent Scsites that can be populated with Cr. The longer average contact lengthsSc—O of the former lead to low energy shifted and broadened emissionbands of Cr(III) compared to the latter modification.

Sc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x)

Emission in the centroid wavelength range 910-970 nm is observed forSc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x) (A=Lu, In, Yb, Tm, Y, Ga, Al; 0<x≤0.75,0≤y≤1.8) if, e.g., excited by green light. These Cr(III) dopedborophosphate materials are characterized by face sharing (Sc,A)₂O₉double octahedra. While not wanting to be bound by any particulartheory, the inventor believes that Cr(III) incorporation into theseuncommon host lattice units leads to the strongly shifted absorption andemission bands towards lower energies compared to host lattices whereCr(III) is incorporated into non-condensed octrahedral structures. As aconsequence, the body color of the claimed Sc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x)phosphors is red (instead of green or yellowish-green as observed forthe disclosed borate and phosphate NIR phosphors).

Sc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x) (A=Lu, In, Yb, Tm, Y, Ga, Al; 0<x≤0.75,0≤y≤1.8) crystallizes in the crystallographic space group P 6₃/m (No176), isotypic with V₂BP₃O₁₂ or in the same space group but isotypic toCr₂BP₃O₁₂ which shows a different arrangement of the otherwise identicalstructural motif.

Sc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x)

Emission in the centroid wavelength range 910-970 nm is observed forSc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x) (A=Lu, In, Yb, Tm, Y, Ga, Al; 0<x≤0.2,0≤y≤2) if, e.g., excited by green light. These Cr(III) dopedsilicophosphate materials are characterized by the same face sharing(Sc,A)₂O₉ double octahedra structure motif as observed for theSc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x) borophosphate phosphors. The crystalstructures are isotypic with V₃SiP₅O₁₉ (“V₃P₅SiO₁₉, avanadosilicophosphate built up from V₂O₉ octahedra clusters, LeClaire etal.” Journal of Solid Stated Chemistry, Volume 65, Issue 2, 15 Nov.1986, Pages 168-177(https://www.sciencedirect.com/science/article/pii/0022459686900514),incorporated by reference herein in its entirety).

Illumination Devices Including the NIR Phosphors

FIG. 1 illustrates a wavelength converting structure 108 that includesat least one of the disclosed luminescent MR phosphor materials.Wavelength converting structure 108 is used in an illumination device101. The light source 100 may be an LED or any other suitable sourceincluding, as examples, resonant cavity light emitting diodes (RCLEDs)and vertical cavity laser diodes (VCSELs). Light source 100 emits afirst light 104. A portion of the first light 104 is incident upon awavelength converting structure 108. The wavelength converting structure108 absorbs the first light 104 and emits second light 112. Thewavelength converting structure 108 may be structured such that littleor no first light is part of the final emission spectrum from thedevice, though this is not required.

Due to the broad band absorbing nature in the visible spectral rangethat the disclosed NIR phosphor materials can be excited with, lightsource 100 may be, for example, blue, green or red emitting LEDs suchas, for example, AlInGaN or AlInGaP or AlInGaAs LEDs.

Wavelength converting structure 108 may include, for example, one ormore of the borate, phosphate, borophosphate, and silicophosphate NIRphosphor materials disclosed herein.

The wavelength converting structure 108 described with respect to FIG. 1can be manufactured, for example, in powder form, in ceramic form, or inany other suitable form. The wavelength converting structure 108 may beformed into one or more structures that are formed separately from andcan be handled separately from the light source, such as a prefabricatedglass or ceramic tile, or may be formed into a structure that is formedin situ with the light source, such as a conformal or other coatingformed on or above the source.

In some embodiments, the wavelength converting structure 108 may bepowders that are dispersed for example in a transparent matrix, a glassmatrix, a ceramic matrix, or any other suitable material or structure.NIR phosphor dispersed in a matrix may be, for example, singulated orformed into a tile that is disposed over a light source. The glassmatrix may be for example a low melting glass with a softening pointbelow 1000° C., or any other suitable glass or other transparentmaterial. The ceramic matrix material can be for example a fluoride saltsuch as CaF₂ or any other suitable material.

The wavelength converting structure 108 may be used in powder form, forexample by mixing the powder NIR phosphor with a transparent materialsuch as silicone and dispensing or otherwise disposing it in a path oflight. In powder form, the average particle size (for example, particlediameter) of the NIR phosphors may be at least 1 μm in some embodiments,no more than 50 μm in some embodiments, at least 5 μm in someembodiments, and no more than 20 μm in some embodiments. Individual NIRphosphor particles, or powder NIR phosphor layers, may be coated withone or more materials such as a silicate, a phosphate, and/or one ormore oxides in some embodiments, for example to improve absorption andluminescence properties and/or to increase the material's functionallifetime.

FIG. 2 illustrates another embodiment in which a wavelength convertingstructure including one or more of the disclosed NIR phosphor materialsmay further be combined with a second phosphor system. In FIG. 2 , thewavelength converting structure 218 includes an NIR phosphor portion 208and a second phosphor portion 202 as part of an illumination device 201.In FIG. 2 , a light source 200 may be an LED or any other suitablesource, (including as examples resonant cavity light emitting diodes(RCLEDs) and vertical cavity laser diodes (VCSELs). Light source 200emits first light 204. First light 204 is incident upon wavelengthconverting structure 218, which includes an NIR phosphor portion 208including one or more of the NIR phosphor materials disclosed herein,and a second phosphor system 202. A portion of the first light 204 isincident on an NIR phosphor portion 208 of the wavelength convertingstructure 218. The NIR phosphor portion 208 absorbs the first light 204and emits second light 212. A portion of the first light 204 is incidenton a second phosphor portion 202 of the wavelength converting structure218. The second phosphor 202 absorbs the first light 204 and emits thirdlight 206. Third light 206 may be visible, though this is not required.The third light 206 is incident on the NIR phosphor portion 208. The NIRphosphor 208 absorbs all or a portion of the third light 206 and emitsfourth light 210.

The wavelength converting structure 218 including an NIR phosphor 208and second phosphor 202 may be structured such that little or no firstlight or third light is part of the final emission spectrum from thedevice, though this is not required.

Due to the broad band absorbing nature in the visible spectral rangethat the disclosed NIR phosphor materials can be excited with, lightsource 200 may be, for example, blue, green or red emitting LEDs suchas, for example, AlInGaN or AlInGaP or AlInGaAs LEDs.

NIR phosphor 208 included in wavelength converting structure 218 mayinclude, for example, one or more of the borate, phosphate,borophosphate, and silicophosphate NIR phosphor materials disclosedherein.

Any suitable second phosphor may be used in the second phosphor system202. In some embodiments, the second phosphor includes one or more of agreen emitting phosphor, a red emitting phosphor and an IR emittingphosphor as disclosed below.

Green Emitting Phosphors for Use as Second Phosphor

Examples of a green emitting phosphor for use in second phosphor portion202 include Sr₄Al₁₄O₂₅:Eu²⁺ and/or A₃B₅O₁₂:Ce³⁺, where A is selectedfrom the group Y, Tb, Gd, and Lu, where B is selected from the group Al,Sc and Ga. In particular, A may at least include one or more of Y andLu, and B at least includes Al. These types of materials may givehighest efficiencies. In an embodiment, the second phosphor includes atleast two luminescent materials of the type of A₃B₅O₁₂:Ce³⁺, where A isselected from the group Y and Lu, where B is selected from the group Al,and where the ratio Y:Lu differ for the at least two luminescentmaterials. For instance, one of them may be purely based on Y, such asY₃Al₅O₁₂:Ce³⁺, and one of them may be a Y,Lu based system, such as(Y_(0.5)Lu_(0.5))₃Al₅O₁₂:Ce³⁺. Compositions of garnets especiallyinclude A₃B₅O₁₂ garnets, where A includes at least yttrium or lutetiumand where B includes at least aluminum. Such garnet may be doped withcerium (Ce), with praseodymium (Pr) or a combination of cerium andpraseodymium; especially however with Ce. Especially, B includesaluminum (Al), however, B may also partly comprise gallium (Ga) and/orscandium (Sc) and/or indium (In), especially up to about 20% of Al, moreespecially up to about 10% of Al (i.e. the B ions essentially consist of90 or more mole % of Al and 10 or less mole % of one or more of Ga, Scand In); B may especially comprise up to about 10% gallium. In anothervariant, B and 0 may at least partly be replaced by Si and N. Theelement A may especially be selected from the group yttrium (Y),gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and/or Tbare especially only present up to an amount of about 20% of A. In aspecific embodiment, the garnet luminescent material includes(Y_(1-x)Lu_(x))₃Al₅O₁₂:Ce, where x is equal to or larger than 0 andequal to or smaller than 1. The terms “:Ce” or “:Ce³⁺” (or similarterms), indicate that part of the metal ions (i.e. in the garnets: partof the “M” ions) in the luminescent material is replaced by Ce (oranother luminescent species when the term(s) would indicate that, like“:Yb”). For instance, assuming (Y_(1-x)Lu_(x))₃Al₅O₁₂:Ce, part of Yand/or Lu is replaced by Ce. This notation is known to the personskilled in the art. Ce will replace M in general for not more than 10%;in general, the Ce concentration will be in the range of 0.1-4%,especially 0.1-2% (relative to M). Assuming 1% Ce and 10% Y, the fullcorrect formula could be (Y_(0.1)Lu_(0.89)Ce_(0.01))₃Al₅O₁₂. Ce ingarnets is substantially or only in the trivalent state, as known to theperson skilled in the art.

Red Emitting Phosphors for Use as Second Phosphor

Examples of a red emitting phosphor for use as second phosphor 202include (Ba,Sr,Ca)AlSiN₃:Eu and(Ba,Sr,Ca)₂Si_(5-x)Al_(x)O_(x)N_(8-x):Eu: In these compounds, europium(Eu) is substantially or only divalent, and replaces one or more of theindicated divalent cations. In general, Eu will not be present inamounts larger than 10% of the cation, especially in the range of about0.5-10%, more especially in the range of about 0.5-5% relative to thecation(s) it replaces. The term “:Eu” or “:Eu²⁺”, indicates that part ofthe metal ions is replaced by Eu (in these examples by Eu²⁺). Forinstance, assuming 2% Eu in CaAlSiN₃:Eu, the correct formula could be(Ca_(0.98)Eu_(0.02))AlSiN₃. Divalent europium will in general replacedivalent cations, such as the above divalent alkaline earth cations,especially Ca, Sr or Ba.

Further, the material (BaSrCa)₂Si_(5-x)Al_(x)O_(x)N_(8-x):Eu can also beindicated as M₂Si_(5-x)Al_(x)O_(x) N_(8-x):Eu, where M is one or moreelements selected from the group barium (Ba), strontium (Sr) and calcium(Ca); especially, M includes in this compound Sr and/or Ba. In a furtherspecific embodiment, M consists of Sr and/or Ba (not taking into accountthe presence of Eu), especially 50-100%, especially 50-90% Ba and 50-0%,especially 50-10% Sr, such as Ba_(1.5)Sr_(0.5)Si₅N₈:Eu, (i.e. 75% Ba;25% Sr). Here, Eu is introduced and replaces at least part of M i.e. oneor more of Ba, Sr, and Ca). Likewise, the material (Sr,Ca,Mg)AlSiN₃:Eucan also be indicated as MAlSiN₃:Eu where M is one or more elementsselected from the group magnesium (Mg) strontium (Sr) and calcium (Ca);especially, M includes in this compound calcium or strontium, or calciumand strontium, more especially calcium. Here, Eu is introduced andreplaces at least part of M (i.e. one or more of Mg, Sr, and Ca).Preferably, in an embodiment the first red luminescent material includes(Ca,Sr,Mg)AlSiN₃:Eu, preferably CaAlSiN₃:Eu. Further, in anotherembodiment, which may be combined with the former, the first redluminescent material includes (Ca,Sr,Ba)₂Si_(5-x)Al_(x)O_(x)N_(8-x):Eu,preferably (Sr,Ba)₂Si₅N₈:Eu. The terms “(Ca,Sr,Ba)” indicate that thecorresponding cation may be occupied by calcium, strontium or barium. Italso indicates that in such material corresponding cation sites may beoccupied with cations selected from the group calcium, strontium andbarium. Thus, the material may for instance comprise calcium andstrontium, or only strontium, etc.

IR Emitting Phosphors for Use as Second Phosphor

Examples of an IR emitting phosphor for use as second phosphor 202include langasite type phosphors of compositionRE₃Ga_(5-x-y)A_(x)SiO₁₄:Cr_(y) (RE=La, Nd, Gd, Yb, Tm; A=Al, Sc) and/orchromium doped garnets of compositionGd_(3-x)RE_(x)Sc_(2-y-z)Ln_(y)Ga_(3-w)Al_(w)O₁₂:Cr_(z) (Ln=Lu, Y, Yb,Tm; RE=La, Nd), where 0≤x≤3; 0≤y≤1.5; 0≤z≤0.3; and 0≤w≤2, and/or one ormore chromium doped colquiirite materials of compositionAAEM_(1-x)F₆:Cr_(x) (A=Li, Cu; AE=Sr, Ca; M=Al, Ga, Sc) where0.005≤x≤0.2, and/or one or more chromium doped tungstate materials ofcomposition A_(2-x)(WO₄)₃:Cr_(x) (A=Al, Ga, Sc, Lu, Yb) where0.003≤x≤0.5.

The wavelength converting structure 218 including NIR phosphor 208 andthe second phosphor 202 described with respect to FIG. 2 can bemanufactured, for example, in powder form, in ceramic form, or in anyother suitable form. The NIR phosphor 208 and the second phosphor 202may be formed into one or more structures that are formed separatelyfrom and can be handled separately from the light source, such as aprefabricated glass or ceramic tile, or may be formed into a structurethat is formed in situ with the light source, such as a conformal orother coating formed on or above the source.

The NIR phosphor 208 and the second phosphor 202 may be mixed togetherin a single wavelength converting layer, or formed as separatewavelength converting layers. In a wavelength converting structure withseparate wavelength converting layers, NIR phosphor 208 and the secondphosphor 202 may be stacked such that the second phosphor 202 may bedisposed between the NIR phosphor 208 and the light source, or the NIRphosphor 208 may be disposed between the second phosphor 202 and thelight source.

In some embodiments, the NIR phosphor 208 and the second phosphor 202may be powders that are dispersed for example in a transparent matrix, aglass matrix, a ceramic matrix, or any other suitable material orstructure. Phosphor dispersed in a matrix may be, for example,singulated or formed into a tile that is disposed over a light source.The glass matrix may be for example a low melting glass with a softeningpoint below 1000° C., or any other suitable glass or other transparentmaterial. The ceramic matrix material can be for example a fluoride saltsuch as CaF₂ or any other suitable material.

The NIR phosphor 208 and second phosphor 202 may be used in powder form,for example by mixing the powder phosphor with a transparent materialsuch as silicone and dispensing or otherwise disposing it in a path oflight. In powder form, the average particle size (for example, particlediameter) of the phosphors may be at least 1 μm in some embodiments, nomore than 50 μm in some embodiments, at least 5 μm in some embodiments,and no more than 20 μm in some embodiments. Individual phosphorparticles, or powder phosphor layers, may be coated with one or morematerials such as a silicate, a phosphate, and/or one or more oxides insome embodiments, for example to improve absorption and luminescenceproperties and/or to increase the material's functional lifetime.

As shown in FIGS. 1 and 2 , an illumination device may include awavelength converting structure that may be used, for example, withlight source 100, 200. Light source 100, 200 may be a light emittingdiode (LED). Light emitted by the light emitting diode is absorbed bythe phosphors in the wavelength converting structure according toembodiments and emitted at a different wavelength. FIG. 3 illustratesone example of a suitable light emitting diode, a III-nitride LED thatemits blue light for use in such an illumination system.

Though in the example below the semiconductor light emitting device is aIII-nitride LED that emits blue or UV light, semiconductor lightemitting devices besides LEDs such as laser diodes and semiconductorlight emitting devices made from other materials systems such as otherIII-V materials, III-phosphide, III-arsenide, II-VI materials, ZnO, orSi-based materials may be used.

FIG. 3 illustrates a III-nitride LED 1 that may be used in embodimentsof the present disclosure. Any suitable semiconductor light emittingdevice may be used and embodiments of the disclosure are not limited tothe device illustrated in FIG. 3 . The device of FIG. 3 is formed bygrowing a III-nitride semiconductor structure on a growth substrate 10as is known in the art. The growth substrate is often sapphire but maybe any suitable substrate such as, for example, SiC, Si, GaN, or acomposite substrate. A surface of the growth substrate on which theIII-nitride semiconductor structure is grown may be patterned,roughened, or textured before growth, which may improve light extractionfrom the device. A surface of the growth substrate opposite the growthsurface (i.e. the surface through which a majority of light is extractedin a flip chip configuration) may be patterned, roughened or texturedbefore or after growth, which may improve light extraction from thedevice.

The semiconductor structure includes a light emitting or active regionsandwiched between n- and p-type regions. An n-type region 16 may begrown first and may include multiple layers of different compositionsand dopant concentration including, for example, preparation layers suchas buffer layers or nucleation layers, and/or layers designed tofacilitate removal of the growth substrate, which may be n-type or notintentionally doped, and n- or even p-type device layers designed forparticular optical, material, or electrical properties desirable for thelight emitting region to efficiently emit light. A light emitting oractive region 18 is grown over the n-type region. Examples of suitablelight emitting regions include a single thick or thin light emittinglayer, or a multiple quantum well light emitting region includingmultiple thin or thick light emitting layers separated by barrierlayers. A p-type region 20 may then be grown over the light emittingregion. Like the n-type region, the p-type region may include multiplelayers of different composition, thickness, and dopant concentration,including layers that are not intentionally doped, or n-type layers.

After growth, a p-contact is formed on the surface of the p-type region.The p-contact 21 often includes multiple conductive layers such as areflective metal and a guard metal which may prevent or reduceelectromigration of the reflective metal. The reflective metal is oftensilver but any suitable material or materials may be used. After formingthe p-contact 21, a portion of the p-contact 21, the p-type region 20,and the active region 18 is removed to expose a portion of the n-typeregion 16 on which an n-contact 22 is formed. The n- and p-contacts 22and 21 are electrically isolated from each other by a gap 25 which maybe filled with a dielectric such as an oxide of silicon or any othersuitable material. Multiple n-contact vias may be formed; the n- andp-contacts 22 and 21 are not limited to the arrangement illustrated inFIG. 4 . The n- and p-contacts may be redistributed to form bond padswith a dielectric/metal stack, as is known in the art.

In order to form electrical connections to the LED 1, one or moreinterconnects 26 and 28 are formed on or electrically connected to then- and p-contacts 22 and 21. Interconnect 26 is electrically connectedto n-contact 22 in FIG. 4 . Interconnect 28 is electrically connected top-contact 21. Interconnects 26 and 28 are electrically isolated from then- and p-contacts 22 and 21 and from each other by dielectric layer 24and gap 27. Interconnects 26 and 28 may be, for example, solder, studbumps, gold layers, or any other suitable structure.

The substrate 10 may be thinned or entirely removed. In someembodiments, the surface of substrate 10 exposed by thinning ispatterned, textured, or roughened to improve light extraction.

Any suitable light emitting device may be used in light sourcesaccording to embodiments of the disclosure. The invention is not limitedto the particular LED illustrated in FIG. 4 . The light source, such as,for example, the LED illustrated in FIG. 4 , is illustrated in thefollowing figures by block 1.

FIGS. 4, 5, and 6 illustrate devices that combine an LED 1 and awavelength converting structure 30. The wavelength converting structure30 may be, for example, wavelength converting structure 108 including anNIR phosphor as shown in FIG. 1 , or wavelength converting structure 218having an NIR Phosphor and a second phosphor as shown in FIG. 2 ,according to the embodiments and examples described above.

In FIG. 4 , the wavelength converting structure 30 is directly connectedto the LED 1. For example, the wavelength converting structure may bedirectly connected to the substrate 10 illustrated in FIG. 4 , or to thesemiconductor structure, if the substrate 10 is removed.

In FIG. 5 , the wavelength converting structure 30 is disposed in closeproximity to LED 1, but not directly connected to the LED 1. Forexample, the wavelength converting structure 30 may be separated fromLED 1 by an adhesive layer 32, a small air gap, or any other suitablestructure. The spacing between LED 1 and the wavelength convertingstructure 30 may be, for example, less than 500 μm in some embodiments.

In FIG. 6 , the wavelength converting structure 30 is spaced apart fromLED 1. The spacing between LED 1 and the wavelength converting structure30 may be, for example, on the order of millimeters in some embodiments.Such a device may be referred to as a “remote phosphor” device.

The wavelength converting structure 30 may be square, rectangular,polygonal, hexagonal, circular, or any other suitable shape. Thewavelength converting structure may be the same size as LED 1, largerthan LED 1, or smaller than LED 1.

Multiple wavelength converting materials and multiple wavelengthconverting structures can be used in a single device. Examples ofwavelength converting structures include luminescent ceramic tiles;powder phosphors that are disposed in transparent material such assilicone or glass that is rolled, cast, or otherwise formed into asheet, then singulated into individual wavelength converting structures;wavelength converting materials such as powder phosphors that aredisposed in a transparent material such as silicone that is formed intoa flexible sheet, which may be laminated or otherwise disposed over anLED 1, wavelength converting materials such as powder phosphors that aremixed with a transparent material such as silicone and dispensed, screenprinted, stenciled, molded, or otherwise disposed over LED 1; andwavelength converting materials that are coated on LED 1 or anotherstructure by electrophoretic, vapor, or any other suitable type ofdeposition.

A device may also include other wavelength converting materials inaddition to the NIR phosphor and a second phosphor described above, suchas, for example, conventional phosphors, organic phosphors, quantumdots, organic semiconductors, II-VI or III-V semiconductors, II-VI orIII-V semiconductor quantum dots or nanocrystals, dyes, polymers, orother materials that luminesce.

The wavelength converting materials absorb light emitted by the LED andemit light of one or more different wavelengths. Unconverted lightemitted by the LED is often part of the final spectrum of lightextracted from the structure, though it need not be. Wavelengthconverting materials emitting different wavelengths of light may beincluded to tailor the spectrum of light extracted from the structure asdesired or required for a particular application.

Multiple wavelength converting materials may be mixed together or formedas separate structures.

In some embodiments, other materials may be added to the wavelengthconverting structure or the device, such as, for example, materials thatimprove optical performance, materials that encourage scattering, and/ormaterials that improve thermal performance.

Examples 1) Synthesis of Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (x=0, 0.2, 0.3)

Compositions of Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (in which x=0, 0.2, 0.3)were synthesized from powders of Sc₂O₃ (5N) obtained from MRE Ltd.,Lu₂O₃ (4N) obtained from Rhodia, Cr₂O₃ (2N) obtained from Alfa Aesar and(NH₄)₂B₁₀O₁₆*4H₂O obtained from Alfa Aesar following the recipes setforth in Table 2:

TABLE 2 recipes for synthesis of Sc_(0.98−x)Lu_(x)BO₃:Cr_(0.02) (x = 0,0.2, 0.3) amounts in gram X Sc₂O₃ (5N) Lu₂O₃ (4N) Cr₂O₃ (2N)(NH₄)₂B₁₀O₁₆*4H₂O 0 65.124 0.0 1.465 56.887 0.2 51.833 38.349 1.46556.887 0.3 45.188 57.524 1.465 56.887

The powders of the Sc₂O₃ (4N), Lu₂O₃ (4N), Cr₂O₃ (2N), and(NH₄)₂B₁₀O₁₆*4H₂O were weighed out according to the amounts shown inTable 2 for each of the x=0, 0.2 and 0.3 Sc_(0.98-x)LU_(x)BO₃:Cr_(0.02)phosphors and combined. Each mixture was then ball mixed in ethanol andfired at 1350° C. for 10 h after drying. After milling, sedimentationfrom water and screening, phosphor powders of each ofSc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (in which x=0, 0.2, 0.3) were obtained.All powders crystallize in the calcite structure type. Table 3summarizes the structure and emission properties of each of theresulting Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (in which x=0, 0.2, 0.3)powders:

TABLE 3 Lattice constants and emission properties ofSc_(0.98−x)Lu_(x)BO₃:Cr_(0.02) (x = 0, 0.2, 0.3) Emission centroidEmission X a (Å) c (Å) wavelength (nm) FWHM (nm) 0 4.7538 15.2831 843.85140.75 0.2 4.7810 15.4483 863.12 158.28 0.3 4.7943 15.5262 863.29 169.61

FIG. 7 shows the emission spectra of each of theSc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (x=0, 0.2, 0.3) phosphors underexcitation of blue light (443 nm). Curve 305 is the emission spectra ofSc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) where x=0.3. Curve 310 is the emissionspectra of Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) where x=0.2. Curve 315 is theemission spectra of Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) where x=0.

2) Synthesis of Sc_(1-x)P₃O₉:Cr_(x) (x=0.02, 0.04, 0.08)

Compositions of Sc_(1-x)P₃O₉:Cr_(x) (in which x=0.02, 0.04, 0.08)phosphors were synthesized from powders of Sc₂O₃ (5N) obtained from MRELtd., Cr₂O₃ (2N) obtained from Alfa Aesar and (NH₄)H₂PO₄ obtained fromMerck following the recipes set forth in Table 4:

TABLE 4 recipes for synthesis of Sc_(1−x)P₃O₉:Cr_(x) (x = 0.02, 0.04,0.08) amounts in gram X Sc₂O₃ (5N) Cr₂O₃ (2N) NH₄H₂PO₄ 0.02 47.92 1.08281.43 0.04 46.95 2.16 281.43 0.08 44.99 4.31 281.43

The powders of the Sc₂O₃ (4N), Cr₂O₃ (2N), and (NH₄) H₂PO₄ were weighedout according to the amounts shown in Table 4 for each of the x=0.02,0.04, 0.08 Sc_(1-x)P₃O₉:Cr_(x) phosphors. The powders were dry mixed bymeans of ball milling followed by firing at 600° C. for 8 hours in air.After intermediate grinding, the powders were re-fired at 800° C. for 8hours in air. Finally, the obtained raw phosphor powders were washedwith water, dried, milled by means of ball milling, and screened.

FIG. 8 shows the powder x-ray diffraction (XRD) pattern of theSc_(0.96)P₃O₉:Cr_(0.04) phosphor. The phosphor is single phase andcrystallizes in the C phase polyphosphate structure (space group C 1 c1).

Table 5 summarizes lattice constants and emission properties of each ofthe resulting Sc_(1-x)P₃O₉:Cr_(x) (in which x=0.02, 0.04, 0.08) powders.

TABLE 5 Lattice constants and Emission properties ofSc_(1−x)P₃O₉:Cr_(0.04) (x = 0.02, 0.04, 0.08) Emission centroid Emissionwavelength FWHM X a (Å) b (Å) c (Å) β (°) (nm) (nm) 0.02 13.5597 19.54079.6925 127.2 908.29 165.09 0.04 13.5525 19.5326 9.6864 127.2 910.39165.51 0.08 13.5322 19.5090 9.6718 127.2 911.17 167.02

FIG. 9 shows the emission spectra of each of the Sc_(1-x)P₃O₉:Cr_(0.04)(x=0.02, 0.04, 0.08) phosphor powders under excitation of blue light(443 nm). Curve 505 is the emission spectra of Sc_(1-x)P₃O₉:Cr_(0.04)where x=0.02. Curve 506 is the emission spectra ofSc_(1-x)P₃O₉:Cr_(0.04) where x=0.04. Curve 507 is the emission spectraof Sc_(1-x)P₃O₉:Cr_(0.04) where x=0.08. Note that the emission spectraare very similar for each compound.

3) Synthesis of Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) (x=0.04, y=0.0; x=0.08,y=0.0; x=0.8, y=0.96)

Compositions of Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) in which (x=0.04, y=0.0;x=0.08, y=0.0; x=0.8, y=0.96) were synthesized from powders of Sc₂O₃(5N) obtained from MIRE Ltd., Ga₂O₃ (4N, UHP grade) obtained fromMolycorp, Cr₂O₃ (2N) obtained from Alfa Aesar, (NH₄)H₂PO₄ obtained fromMerck, and (NH₄)₂B₁₀O₁₆*4H₂O obtained from Alfa Aesar following therecipes set forth in Table 6:

TABLE 6 recipes for synthesis of Sc_(2−x−y)Ga_(y)BP₃O₁₂:Cr_(x) amountsin gram x/y Sc₂O₃ (5N) Ga₂O₃ (4N) Cr₂O₃ (2N) NH₄H₂PO₄ (NH₄)₂B₁₀O₁₆*4H₂O0.04/0.0 70.093 0.0 1.577 205.809 30.614 0.08/0.0 68.662 0.0 3.153205.809 30.614  0.08/0.96 31.049 42.201 2.852 186.133 28.794

The powders of the Sc₂O₃ (4N), Ga₂O₃ (4N), Cr₂O₃ (2N), (NH₄) H₂PO₄, and(NH₄)₂B₁₀O₁₆*4H₂O weighed out according to the amounts shown in Table 6for each of the x=0.04, y=0.0; x=0.08, y=0.0; x=0.8, y=0.96Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) phosphors were combined. The powdermixtures according to the recipes given in Table 6 were then obtained byball milling. Firing was carried out at 600° C. for 8 hours followed bypowderization. After a second firing at 1200° C., the raw phosphor wasball milled and screened.

FIG. 10 shows the X-ray powder diffraction patterns of the resultingSc_(1.96)BP₃O₁₂:Cr_(0.04). The pattern shows that theSc_(1.96)BP₃O₁₂:Cr_(0.04) material crystallized hexagonally in thecrystallographic space group P 6₃/m (No 176), isotypic with V₂BP₃O₁₂.

Table 7 summarizes the lattice constants and emission properties of eachof the Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) in which (x=0.04, y=0.0; x=0.08,y=0.0; x=0.8, y=0.96) phosphors under blue light excitation.

TABLE 7 Lattice constants and emission properties ofSc_(2−x−y)Ga_(y)BP₃O₁₂:Cr_(x) Emission centroid Emission x/y a (Å) c (Å)wavelength (nm) FWHM (nm) 0.04/0.0 14.2294 7.7240 931.92 171.3 0.08/0.014.2233 7.7153 936.02 169.82  0.8/0.96 14.1554 7.6408 933.12 173.46

As examples, FIG. 11 shows the diffuse reflectance ofSc_(1.92)BP₃O₁₂:Cr_(0.08) phosphor powder, and FIG. 12 shows theemission spectra of Sc_(1.92)BP₃O₁₂:Cr_(0.08) under excitation at 443nm.

4) Synthesis of Sc_(2.88)SiP₅O₁₉:Cr_(0.12)

Compositions of Sc_(2.88)SiP₅O₁₉:Cr_(0.12) were synthesized from powdersof Sc₂O₃ (5N, obtained from MRE Ltd.), Cr₂O₃ (2N, obtained from AlfaAesar), SiO₂ (Aerosil®, obtained from Evonik) and NH₄H₂PO₄ (p.a.,obtained from Merck) following the recipe set forth in Table 8.

TABLE 8 Powder Sc₂O₃ Cr₂O₃ SiO₂ NH₄H₂PO₄ Amount in grams 63.875 2.93323.309 188.685

The powders of Sc₂O₃, Cr₂O₃, SiO₂, and NH₄H₂PO₄ weighed out according tothe amounts in Table 8 were mixed and fired in air at 600° C. Aftergrinding, the mixture was further fired under CO atmosphere at 1350° C.for 4 hrs. The resulting powder phosphor was ball milled and washed withwater, followed by drying.

FIG. 13 shows the powder X-ray diffraction pattern of the sample ofSc_(2.88)SiP₅O₁₉:Cr_(0.12). Sc_(2.88)SiP₅O₁₉:Cr_(0.12) crystallizes inthe V₃SiP₅O₁₂ structure type (Space group P 6₃, No. 173) with latticeconstants a₀=14.713 Å and c₀=7.702 Å. The reflections marked with anasterisk (*) in FIG. 13 belong to ScP₃O₉ as an impurity phase. FIG. 14is the corresponding emission spectrum of the Sc_(2.88)SiP₅O₁₉:Cr_(0.12)under 443 nm excitation.

5) Illumination Device with a Wavelength Converting Structure Includingan NIR Phosphor

A wavelength converting structure including the NIR phosphors was formedand included in an illumination device. To form the wavelengthconverting structure, 5 wt % Sc_(0.98)BO₃:Cr_(0.02) and 95 wt %Sc_(1.92)BP₃O₁₂:Cr_(0.08) were mixed into a curable silicone polymer.The mixture was filled into leadframe packages containing 450 nmemitting InGaN LEDs with a phosphor/silicone weight ratio of 2 to formthe pc NIR LED illumination device.

FIG. 15 shows an EL spectrum of the obtained pc NIR LED. The EL spectrumis characterized by an even spectral power distribution in the 750-1050nm range.

6) Synthesis of Sc_(0.78)In_(0.2)BO₃:Cr_(0.02)

5.183 g scandium oxide (MRE Ltd., 4N), 0.146 g chromium (III) oxide(Alfa Aesar, 99%), 5.691 g ammonium borate hydrate (NH₄)₂B₁₀O₁₆*4 H2O(Alfa Aesar, 98%) and 3.837 g indium oxide (Auer Remy, 5N) are mixed byplanetary ball milling and fired at 1200° C. for 10 hrs in a coveredalumina crucible. After grinding, washing with water and ethanol andfinal screening the powder phosphor was obtained. X-ray diffractionshows that the material crystallizes in the calcite structure type. Thefollowing Table 9 lists lattice constants and emission properties.

TABLE 9 Emission centroid Emission a (Å) c (Å) wavelength (nm) FWHM (nm)4.7752 15.3411 845.19 142.68

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single element or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage.

Any (later) reference signs in the claims should not be construed aslimiting the scope.

The following enumerated clauses provide additional non-limiting aspectsof the disclosure.

1. A luminescent material comprising Sc_(1-x-y)A_(y)MO:Cr_(x), whereinMO=P₃O₉, (BP₃O₁₂)_(0.5), (SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al,where 0<x≤0.75, 0≤y≤1.

2. The luminescent material of clause 1, wherein MO is P₃O₉ and 0<x≤0.5,0≤y≤0.9.

3. The luminescent material according to any one of the precedingclauses, comprising Sc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x), wherein A=Lu, In, Yb,Tm, Y, Ga, Al; 0<x≤0.75, 0≤y≤1.8.

4. The luminescent material according to any one of the precedingclauses, comprising Sc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In, Yb,Tm, Y, Ga, Al; 0<x≤0.2, 0≤y≤2.

5. The luminescent material according to any one of the precedingclauses, wherein the luminescent material emits light having a peakwavelength in a range of 700 nm to 1100 nm.

6. A wavelength converting structure comprising an NIR phosphormaterial, the NIR phosphor material including at least one ofSc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=BO₃, P₃O₉, (BP₃O₁₂)_(0.5),(SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al, where 0<x≤0.75, 0≤y≤1,and wherein when MO=BO₃, 0<y.

7. The wavelength converting structure of clause 6, further comprising alight source emitting a first light, the wavelength converting structuredisposed in a path of the first light, wherein the NIR phosphor absorbsthe first light and emits a second light, the second light having awavelength range of 700 nm to 1100 nm.

8. The wavelength converting structure according to any one of thepreceding clauses 6-7, further comprising a second phosphor material,wherein the second phosphor material includes at least one of a greenphosphor, a red phosphor, and an IR phosphor.

9. The wavelength converting structure according to any one of thepreceding clauses 6-8, wherein MO is P₃O₉ and 0<x≤0.5, 0≤y≤0.9.

10. The wavelength converting structure according to any one of thepreceding clauses 6-9, wherein the NIR phosphor comprisesSc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al;0<x≤0.75, 0≤y≤1.8.

11. The wavelength converting structure according to any one of thepreceding clauses 6-10, wherein the NIR phosphor comprisesSc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al;0<x≤0.2, 0≤y≤2.

12. The wavelength converting structure according to any one of thepreceding clauses 6-11, wherein MO is BO₃, 0<x≤0.5, y>0 and y≤0.9.

13. The wavelength converting structure according to any one of thepreceding clauses 6-12, wherein the MO is BO₃, A is Lu and 0.05≤y≤0.25and 0.01≤x≤0.06.

14. The wavelength converting structure according to any one of thepreceding clauses 6-13, wherein the NIR phosphor includes at least oneof Sc_(0.98-x)Lu_(x)BO₃:Cr_(0.02) (x=0, 0.2, 0.3), Sc_(1-x)P₃O₉:Cr_(x)(x=0.02, 0.04, 0.08), Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x) (x=0.04, y=0.0;x=0.08, y=0.0; x=0.8, y=0.96), and Sc_(2.88)SiP₅O₁₉:Cr_(0.12).

15. The wavelength converting structure according to any one of thepreceding clauses 6-14, wherein the NIR phosphor includes 5 wt %Sc_(0.98)BO₃:Cr_(0.02) and 95 wt % Sc_(1.92)BP₃O₁₂:Cr_(0.08).

The invention claimed is:
 1. A luminescent material comprisingSc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=P₃O₉, (BP₃O₁₂)_(0.5), or(SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al or a mixture thereof,where 0<x≤0.75, 0≤y≤1.
 2. The luminescent material of claim 1, whereinMO is P₃O₉ and 0<x≤0.5, 0≤y≤0.9.
 3. The luminescent material accordingto claim 1, comprising Sc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x), wherein A=Lu, In,Yb, Tm, Y, Ga, Al or a mixture thereof; 0<x≤0.75, 0≤y≤1.8.
 4. Theluminescent material according to claim 2, comprisingSc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof; 0<x≤0.75, 0≤y≤1.8.
 5. The luminescent materialaccording to claim 1, comprising Sc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), whereinA=Lu, In, Yb, Tm, Y, Ga, Al or a mixture thereof; 0<x≤0.2, 0≤y≤2.
 6. Theluminescent material according to claim 2, comprisingSc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof; 0<x≤0.2, 0≤y≤2.
 7. The luminescent material accordingto claim 3, comprising Sc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In,Yb, Tm, Y, Ga, Al or a mixture thereof; 0<x≤0.2, 0≤y≤2.
 8. Theluminescent material according to claim 4, comprisingSc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof; 0<x≤0.2, 0≤y≤2.
 9. The luminescent material accordingto claim 1, wherein the luminescent material emits light having a peakwavelength in a range of 700 nm to 1100 nm.
 10. A wavelength convertingstructure comprising an NIR phosphor material, the NIR phosphor materialincluding at least one of Sc_(1-x-y)A_(y)MO:Cr_(x), wherein MO=P₃O₉,(BP₃O₁₂)_(0.5), or (SiP₅O₁₉)_(0.34); A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof, where 0<x≤0.75, 0≤y≤1.
 11. The wavelength convertingstructure according to claim 10, further comprising a second phosphormaterial, wherein the second phosphor material includes at least one ofa green phosphor, a red phosphor, and an IR phosphor.
 12. The wavelengthconverting structure according to claim 10, wherein MO is P₃O₉ and0<x≤0.5, 0≤y≤0.9.
 13. The wavelength converting structure according toclaim 10, wherein the NIR phosphor comprisesSc_(2-x-y)A_(y)BP₃O₁₂:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof; 0<x≤0.75, 0≤y≤1.8.
 14. The wavelength convertingstructure according to claim 10, wherein the NIR phosphor comprisesSc_(3-x-y)A_(y)SiP₅O₁₉:Cr_(x), wherein A=Lu, In, Yb, Tm, Y, Ga, Al or amixture thereof; 0<x≤0.2, 0≤y≤2.
 15. The wavelength converting structureaccording to claim 10, wherein the NIR phosphor includes at least one ofSc_(1-x)P₃O₉:Cr_(x) (x=0.02, 0.04, 0.08), Sc_(2-x-y)Ga_(y)BP₃O₁₂:Cr_(x)(x=0.04, y=0.0; x=0.08, y=0.0; x=0.8, y=0.96), andSc_(2.88)SiP₅O₁₉:Cr_(0.12).
 16. The wavelength converting structureaccording to claim 10, wherein the NIR phosphor includes 5 wt %Sc_(0.98)BO₃:Cr_(0.2) and 95 wt % Sc_(1.92)BP₃O₁₂:Cr_(0.08).
 17. A lightemitting device comprising: a light source emitting a first light; andthe wavelength converting structure of claim 10 disposed in a path ofthe first light, the NIR phosphor in the wavelength converting structureemitting a second light having a wavelength range of 700 nm to 1100 nmin response to absorbing first light.
 18. The light emitting device ofclaim 17, wherein the wavelength converting structure comprises a secondphosphor material that includes at least one of a green phosphor, a redphosphor, and an IR phosphor.